The ERS/Envisat (A)ATSR dataset is available through the ATSR MERCI system.
Both http and ftp access are available to this product set that has been processed with the same algorithm and so represents a homogeneous product set from August 1991 to April 2012 (ref 3rd reprocessing).
FTP users can download all ATSR-1, ATSR-2 and AATSR Level-1b and Level-2 products in Envisat format (TOA_1P, NR_2P, AR_2P and MET_2P).
Additionally, FTP users also have access to the L2P and L3U products providing (A)ATSR data in NetCDF-4 format.
For all three ATSR instruments, Level-1b and Level-2 products (TOA_1P and NR_2P) can also be browsed through the ATSR MERCI interface which allows users to select geographical areas of interest and search for products for specific periods of time.
See related news on the (A)ATSR 3rd Reprocessing of 13 December 2013.